Problem: $ \left(\dfrac{9}{25}\right)^{-\frac{1}{2}}$
Answer: $= \left(\dfrac{25}{9}\right)^{\frac{1}{2}}$ Figure out what goes in the blank: $\Big(? \Big)^{2}=\dfrac{25}{9}$ Figure out what goes in the blank: $\Big({\dfrac{5}{3}}\Big)^{2}=\dfrac{25}{9}$ So $\left(\dfrac{9}{25}\right)^{-\frac{1}{2}}=\left(\dfrac{25}{9}\right)^{\frac{1}{2}}=\dfrac{5}{3}$